|Origin:||surveiller 'to watch over', from sur- ( SURCHARGE) + veiller 'to watch' (from Latin vigil; VIGIL)|
when the police, army, etc watch a person or place carefully because they may be connected with criminal activities
24-hour surveillance of the building
They were under constant close surveillance day and night.
The suspects were kept under surveillance.
electronic surveillance equipment
when one country watches the military activities of another country to see what they are planning to do:
a surveillance mission
when doctors, health departments etc watch an ill person or watch the development of a disease in a population
Diane was placed under psychiatric surveillance.